Loss of circadian rhythmicity in blood testosterone levels with aging in normal men

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Abstract

Previous studies concerning the relationship of serum testosterone levels
to aging in normal men have yielded apparently inconsistent results.
Studies performing blood sampling in the morning have often shown an
age-related decrease in testosterone levels, while those using afternoon
samples have failed to show such a decrease. These results suggested to us
the possibility that the circadian rhythm in serum testosterone levels
might be altered with normal aging in men. Hourly blood samples were
obtained for 24 h from 1 young (mean age, 52.2 yr) and 12 old (mean age,
17 yr) healthy men. Total testosterone levels were measured by RIA. The
circadian rhythm in serum testosterone levels found in normal young men
was markedly attenuated or absent in healthy elderly men; the early
morning rise in testosterone levels characteristic of young men was not
present in old age. Mean testosterone levels for the entire 24-h day were
lower in healthy old men than in young men. These results demonstrate a
clear decrease in serum testosterone levels in healthy old men compared to
those in young men and provide an explanation for the inability to
demonstrate an age-related decline in testosterone levels in earlier
studies using serum samples obtained in the afternoon.